Wide-angle aspheric zoom lens

Abstract: A first lens group (1) having a negative refracting power and a second lens group (1) having a positive refracting power are arranged in order from the photographing object side, zooming is performed by changing the aerial interval between the first and second lens groups, both the first and second lens groups have one or more aspheric surfaces, and the first lens group comprises two negative lenses (L1,L2) positive lens (L3) which are arranged in order from the object side and the second lens group comprises a positive lens (L4), a cemented lens (L5,L6) comprising a positive lens (L5) and a negative lens (L6), and a positive lens (L7) which are arranged in order from the object side.

Description: Background of the Invention 1. Field of the Invention The present invention relates to a high-performance wide-angle aspheric zoom lens used for a video camera or the like, having a zoom ratio of approx. 3, a half angle of view of approx. 40° at the wide-angle end, and aberration correction. 2. Related art of the Invention High image quality and high performance as well as operability and maneuverability are being demanded from the latest video cameras. Because of this, 1/3 inch high-resolution imaging devices have become popular and 1/4 inch imaging devices are now being developed. Thus, these devices have contributed to the decrease in size and weight of video cameras. In addition, a compact lightweight high-performance wide-angle zoom lens with a large aperture ratio is strongly in demand. Moreover, a decrease in cost is also strongly desired. Therefore, it is necessary to develop a high-performance wide-angle zoom lens comprised of fewer lenses that is machinable and has superior mass production characteristics. For a high-magnification wide-angle zoom lens, however, the outside diameter of the lens closest to an object increases; moreover several lenses are required to achieve high aberration correction. The size, weight, and price of the zoom lenses increase and therefore zoom lenses cannot be used in consumer video cameras. For compact and lightweight zoom lenses with a zoom ratio of 2 to 3 and comprising fewer lenses, a two-group zoom lens is frequently used which zooms an object by arranging a lens group with a negative refracting power at the object side and a lens group with a positive refracting power at the image side and changing the distance between both lens groups. For example, the two-group zoom lens disclosed in U.S. Patent No. 5155629 has a zoom ratio of approx. 3, a half angle of view of 27° to 9° , and an F number of 2.8 to 5.7, comprising 7 to 8 lenses. The two-group zoom lens disclosed in Japanese Patent Publication No. Hei 3-16004 has a zoom ratio of approx. 2, a half angle of view of approx. 38° to 17°, and an F number of 4 to 4.5, comprising 10 lenses. In U.S. Patent No. 5 054 897 a two group lens with a zoom ratio of 2 a half angle of view at the wide angle zoom position of 27° and a F-number at the wide angle zoom position of 2 is described having 7 components. However, the existing two-group zoom lenses having the above constitution cannot simultaneously have a zoom ratio of approx. 3, a half angle of view of approx. 38°, and an F number of 2 because the lens comprises a small number of lenses. Summary of the Invention The present invention is designed to solve the above problems with existing zoom lenses and its object is to provide a wide-angle aspheric zoom lens with a simple structure having various types of aberration correction including chromatic aberration and a zoom ratio of approx. 3 by using a new lens structure and the optimum aspheric arrangement and also provide a video camera using the wide-angle aspheric zoom lens. This object is achieved by a wide-angle aspheric zoom lens having the features of claim 1 and a video camera according to claim 2. The present invention provides a machinable wide-angle aspheric zoom lens comprising the above simple structure and having a zoom ratio of approx. 3, a half angle of view of approx. 40° at the wide angle end, and an F number of approx. 2 by constituting the first lens group with two negative lenses and a positive lens and the second lens group with a positive lens, a cemented lens comprising a positive lens and a negative lens, and a positive lens, and forming one or more aspheric surfaces in both the first and second lens groups. Moreover, the present invention provides a high-performance wide-angle aspheric zoom lens with a simple structure having aberration correction by meeting conditions (1) to (6). Furthermore, by meeting condition (7) or (8), it is possible to use the forming method which is superior in mass production characteristics and also decreases the forming time while realizing an accurate surface shape. Furthermore, by using the wide-angle zoom lens of the present invention, it is possible to realize a compact, lightweight, high-magnification, and high-image-quality video camera. As described above, the wide-angle aspheric zoom lens of the present invention makes it possible to realize, for example, a zoom ratio of approx. 3, a half angle of view of approx. 40° at the wide angle end, and an F number of approx. 2 by using a simple machinable structure comprising 7 lenses and also to realize a compact lightweight high-performance video camera. Brief Description of the Drawings Fig. 1 shows a block diagram of the wide-angle aspheric zoom lens of the first embodiment of the present invention; Figs. 2, 3, and 4 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the first embodiment of the present invention respectively; Figs. 5, 6, and 7 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the second embodiment of the present invention respectively; Figs. 8, 9, and 10 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the third embodiment of the present invention respectively; Figs. 11, 12, and 13 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the fourth embodiment of the present invention respectively; Figs. 14, 15, and 16 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the fifth embodiment of the present invention respectively; Figs. 17, 18, and 19 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the sixth embodiment of the present invention respectively; Figs. 20, 21, and 22 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the seventh embodiment of the present invention respectively; Figs. 23, 24, and 25 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the eighth embodiment of the present invention respectively; Figs. 26, 27, and 28 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the ninth embodiment of the present invention respectively; Figs. 29, 30, and 31 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the tenth embodiment of the present invention respectively; Figs. 32, 33, and 34 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the wide-angle aspheric zoom lens of the eleventh embodiment of the present invention respectively; Fig. 35 shows an illustration of the structure of the video camera of the present invention. In each aberration diagram, (a), (b), (c), (d), and (e) represent spherical aberration, astigmatism, distortion (%), chromatic spherical aberration, and chromatic aberration of magnification respectively. In the diagram of spherical aberration, a continuous line represents the spherical aberration of the d-line and the dashed line represents the sin condition. In the diagram of astigmatism, a continuous line represents the sagittal image surface curvature and the dashed line represents the meridional image surface curvature. In the diagram of chromatic spherical aberration, the continuous line represents the value for the d-line, the dashed line represents the value for the F-line, and the broken line represents the value for the C-line. In the diagram of chromatic aberration of magnification , the dashed line represents the value for the F-line and the broken line represents the value for the C-line. 1...First lens group 2...Second lens group 3...Crystal filter or the like 4...Image formation surface Description of Preferred Embodiments Embodiments of the present invention are described below by referring the accompanying drawings. Fig. 1 shows a block diagram of the first embodiment of the wide-angle aspheric zoom lens of the present invention. In Fig. 1, a first lens group 1, a second lens group 2, a flat plate 3 optically equivalent to a crystal filter or a face plate of an imaging device, and an image surface 4 are arranged in order from the left. Zooming is performed by changing the aerial interval between the first lens group 1 having a negative refracting power and the second lens group 2 having a positive refracting power. When necessary, focusing is performed by moving the first lens group 1 along the optical axis or moving both the first lens group 1 and the second lens group 2 along the optical axis. The first lens group 1 has one or more aspheric surfaces and comprises two negative lenses and a positive lens and the second lens group 2 has one or more aspheric surfaces and comprises a positive lens, a cemented lens comprising a positive lens and a negative lens, and a positive lens. The first lens group comprises two meniscus negative lenses L1 and L2 whose image sides are concave and the meniscus positive lens L3 whose image side is concave which are arranged in order from the photographing object side and has one or more aspheric surfaces are indispensable to constitute the first lens group 1 with three lenses, realize a half angle of view of approx. 40° , and correct various types of aberrations. Particularly, the aspheric surface of the first lens group 1 is very effective to correct a distortion. Each condition of the first lens group 1 is described below in more detail. Condition (1) deals with the refracting power of the first lens group 1. When the refracting power exceeds an upper limit, the lateral magnification of the second lens group 2 increases, the F number at the narrow-angle side increases, and it is more difficult to correct an aberration. On the contrary, when the refracting power exceeds a lower limit, the lateral magnification of the second lens group 2 decreases, it is more difficult to secure the back focus necessary for insertion of a crystal filter, and the overall lens length and the outside diameter of the lenses of the first lens group 1 increase. Condition (2) deals with the average value of radiuses of curvature at the image-side surface of lens L1 and that of lens L2. When the average value exceeds a lower limit, the spherical aberration of the narrow-angle side is excessively corrected and it is more difficult to machine lenses because of too large a curvature. When the average value exceeds an upper limit, it is impossible to simultaneously correct the astigmatism and distortions only by optimizing the aspheric surface. Condition (3) deals with the radius of curvature of the object-side surface of lens L3. When the radius of curvature exceeds a lower limit, it is more difficult to correct the spherical aberration at the narrow-angle side and also more difficult to machine lenses because of too large a radius of curvature. When the radius of curvature exceeds an upper limit, it is more difficult to correct the coma aberration produced in lenses L1 and L2. Condition (4) deals with the Abbe numbers of lenses L1, L2, and L3 constituting the first lens group 1. When the Abbe number exceeds a lower limit, it is impossible to correct the chromatic aberration of magnification at the wide-angle side. Moreover, it is difficult to simultaneously correct the chromatic spherical aberration and chromatic aberration of magnification at the narrow-angle side. The conditions in the second lens group comprises the positive lens L4 whose object and image sides are convex, the cemented lens comprising the positive lens L5 whose object side is convex and the negative lens L6 whose image side is concave, and the positive lens L7 whose object side is convex which are arranged in order from the object side, and has one or more aspheric surfaces are indispensable to constitute the second lens group 2 with four lenses, realize a large aperture ratio of approx. F 2 at the wide-angle side and approx. F 3 at the narrow-angle side, and correct various types of monochromatic aberrations and the chromatic aberration. Particularly, the aspheric surface of the second lens group 2 is very effective to correct the spherical aberration. The condition that the object-side surface and the image-side surface of the positive lens L5 which is the second lens from the object side of the second lens group 2 or the positive lens L7 which is the fourth lens from the object side of it have the same radius of curvature provides a large advantage in manufacturing a zoom lens comprising a small lens whose object- and image-side radiuses of curvature are very difficult to differentiate is not inversely inserted when assembling the zoom lens. Each condition of the second lens group 2 is described below in more detail. Condition (5) deals with the radius of curvature of the object-side surface of lens L5. When the radius of curvature exceeds a lower limit, the coma aberration, which is higher than the principal ray, is excessively corrected for an object point lower than the optical axis and it is more difficult to machine the lens because of too large radius of curvature. When the radius of curvature exceeds an upper limit, it is more difficult to secure the back focus necessary for insertion of a crystal filter or the like because the position of the image-side principal point of the second lens group 2 approaches the object side. Condition (6) deals with the radius of curvature of the image-side surface of lens L7. When the radius of curvature exceeds a lower limit, a large flare due to the coma aberration upper than the principal ray is produced for an object point lower than the optical axis and it is more difficult to machine the lens because of too large radius of curvature. When the radius of curvature exceeds an upper limit, it is more difficult to correct the astigmatism. Table 1 shows concrete numerical values. In Table 1, symbol "r" represents the radius of curvature of a lens surface, "d" represents the thickness of a lens or the aerial interval between lenses, "n" represents the refractive index for d-line of each lens, "ν" represents the Abbe number for the d-line of each lens. The aspheric surface is defined as the following expression (1). Z = CY 2 1+ 1-C 2 Y 2 + D·Y 4 + E·Y 6 + F·Y 8 + G·Y 10 Z: Distance of point on aspheric surface from aspheric surface apex when height from the optical axis equals Y Y: Height from optical axis C: Curvature of aspheric surface apex D, E, F, and G: Aspheric surface factor The first and eighth surfaces are aspheric and the aspheric surface factor is shown in Table 2. Table 3 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming. Table 4 shows the value of each conditional expression. In these tables, the standard position is a zoom position for the minimum lens length. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 5 shows the second numerical embodiment The first, eighth, and ninth surfaces are aspheric and the aspheric surface factor of each surface is shown in Table 6. Table 7 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming. Table 8 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 9 shows the third numerical embodiment. The first and eighth surfaces are aspheric and the aspheric factor is shown in Table 10. Table 11 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 12 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 13 shows the fourth numerical embodiment. The third and eighth surfaces are aspheric and the aspheric surface factor is shown in Table 14. Table 15 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 16 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 17 shows the fifth numerical embodiment. The first and tenth surfaces are aspheric and the aspheric surface factor is shown in Table 18. Table 19 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 20 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 21 shows the sixth numerical embodiment. The first, eighth, and ninth surfaces are aspheric and the aspheric surface factor is shown in Table 22. Table 23 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 24 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 25 shows the seventh numerical embodiment. The first, eighth, and ninth surfaces are aspheric and the aspheric surface factor is shown in Table 26. Table 27 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 28 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 29 shows the eighth numerical embodiment which is a concrete numerical example for meeting condition (7) of the center thickness dl of lens L1 of the first lens group. The first, eighth, and ninth surfaces are aspheric and the aspheric surface factor is shown in Table 30. Table 31 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 32 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 33 shows the ninth numerical embodiment which is another concrete numerical example for meeting condition (7). The first, eighth, and ninth surfaces are aspheric and the aspheric surface factor is shown in Table 34. Table 35 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 36 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 37 shows the tenth numerical embodiment which is still another concrete numerical example for meeting condition (7). The first, eighth, and ninth surfaces are aspheric and the aspheric surface factor is shown in Table 38. Table 39 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 40 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Table 41 shows the eleventh numerical embodiment which is a concrete numerical example for meeting condition (8) of the center thickness d3 of lens L2 of the first lens group. The third and eighth surfaces are aspheric and the aspheric surface factor is shown in Table 42. Table 43 shows the value for an object point at a position 2 m from the lens tip as an example of the aerial interval which can be changed by zooming and Table 44 shows the value of each conditional expression. Symbols f, F/NO, and W represent the focal length, F number, and half angle of view at each zoom position respectively. Figs. 2, 3, and 4 show aberration diagrams at the wide-angle-end, standard position, and telephoto end zoom positions of the aspheric zoom lens of the first embodiment shown in Table 1 respectively. Figs. 5, 6, and 7 show aberration performances of the aspheric zoom lens of the second embodiment shown in Table 5 respectively; Figs. 8, 9, and 10 show aberration performances of the aspheric zoom lens of the third embodiment shown in Table 9 respectively; Figs. 11, 12, and 13 show aberration performances of the aspheric zoom lens of the fourth embodiment shown in Table 13 respectively; Figs. 14, 15, and 16 show aberration performances of the aspheric zoom lens of the fifth embodiment shown in Table 17 respectively; Figs. 17, 18, and 19 show aberration performances of the aspheric zoom lens of the sixth embodiment shown in Table 21 respectively; Figs. 20, 21, and 22 show aberration performances of the aspheric zoom lens of the seventh embodiment shown in Table 25 respectively; Figs. 23, 24, and 25 show aberration performances of the aspheric zoom lens of the eighth embodiment shown in Table 29 respectively; Figs. 26, 27, and 28 show aberration performances of the aspheric zoom lens of the ninth embodiment shown in Table 33 respectively; Figs. 29, 30, and 31 show aberration performances of the aspheric zoom lens of the tenth embodiment shown in Table 37 respectively; and Figs. 32, 33, and 34 show aberration performances of the aspheric zoom lens of the eleventh embodiment shown in Table 41 respectively. From these figures, it is found that each embodiment has a preferable optical performance in which both the monochromatic aberration and the chromatic aberration are well corrected. The video camera of the present invention, as shown in Fig. 35, comprises at least the wide-angle aspheric zoom lens 11, imaging device 12, signal processing circuit 13, and view finder 14 of the above embodiments. Therefore, it is possible to realize a compact lightweight high-performance video camera. In the above description, a case is described in which the object-side surface of lens L1 or L2 of the first lens group 1 is aspheric. However, it is also possible to apply the present invention to a case in which the other surface is aspheric. In the above description, a case is described in which lens L4 or L5 of the second lens group 2 is aspheric. However, it is also possible to apply the present invention to a case in which the other surface is aspheric. First embodiment Group Surface r d n ν 1 1 19.224 1.00 1.67790 55.5 2 6.088 1.78 3 15.522 0.80 1.77250 49.6 4 4.702 1.59 5 6.364 2.00 1.80518 25.5 6 10.423 Variable 7 1.00 2 8 5.898 2.30 1.60311 60.7 9 -15.228 0.10 10 6.820 2.40 1.58913 61.2 11 -6.813 0.70 1.71736 29.5 12 3.521 0.41 13 9.259 1.40 1.64769 33.9 14 -23.627 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of first embodiment Surface 1 8 D 2.632E-4 -7.416E-4 E 1.277E-6 -3.294E-6 F -5.798E-8 -1.715E-6 G 1.685E-9 7.732E-8 Zoom interval of first embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 7.481 8.672 F/NO 2.061 2.954 3.198 d6 13.072 2.646 1.688 d14 1.000 5.170 6.281 Value of conditional expression of first embodiment fW/|f1| 0.40 (r2+r4)/2/|f1| 0.72 r5/|f1| 0.85 (νL1+νL2)/2-νL3 27.1 r10/f2 0.98 r12/f2 0.51 Second embodiment Group Surface r d n ν 1 1 21.638 1.00 1.72000 50.3 2 6.101 1.54 3 29.470 0.80 1.77250 49.6 4 4.592 1.75 5 7.155 2.00 1.80518 25.5 6 14.443 Variable 7 1.00 2 8 6.013 2.50 1.58904 53.2 9 -13.033 0.10 10 16.018 2.20 1.58913 61.2 11 -16.330 0.60 1.75520 27.5 12 4.478 0.28 13 7.231 1.80 1.54072 47.2 14 -10.888 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of second embodiment Surface 1 8 9 D 3.520E-4 -9.794E-4 -2.321E-5 E 5.763E-6 -1.668E-5 -2.013E-5 F -2.113E-7 -1.536E-6 -1.278E-6 G 4.373E-9 -2.046E-7 -1.492E-7 Zoom interval of second embodiment for 2-m object point Wide-angle end Standard positions Telephoto end f 3.001 6.253 8.681 F/NO 2.058 2.714 3.434 d6 12.275 3.781 1.589 d14 1.000 4.670 7.715 Value of conditional expression of second embodiment fW/|f1| 0.48 (r2+r4)/2/|f1| 0.85 r5/|f1| 1.41 (νL1+νL2)/2-νL3 25.5 r10/f2 2.05 r12/f2 0.57 Third embodiment Group Surface r d n ν 1 1 14.000 1.00 1.67790 55.5 2 6.364 1.96 3 13.381 0.80 1.71300 53.9 4 4.879 2.48 5 6.323 2.00 1.80518 25.5 6 7.698 Variable 7 1.00 2 8 6.619 2.00 1.60311 60.7 9 -16.017 0.10 10 5.907 2.60 1.58913 61.2 11 -12.369 0.70 1.74000 28.2 12 3.479 0.47 13 12.440 1.40 1.60342 38.0 14 -14.102 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of third embodiment Surface 1 8 D 2.081E-4 -6.006E-4 E -1.412E-6 -1.794E-6 F 6.306E-8 -1.346E-6 G 4.72E-12 6.656E-8 Zoom interval of third embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 8.416 8.659 F/NO 2.075 3.064 3.109 d6 14.655 1.835 1.636 d14 1.000 5.549 5.754 Value of conditional expression of third embodiment fW/|f1| 0.36 (r2+r4)/2/|f1| 0.66 r5/|f1| 0.75 (νL1+νL2)/2-νL3 29.2 r10/f2 0.84 r12/f2 0.49 Fourth embodiment Group Surface r d n ν 1 1 17.145 1.00 1.67790 55.5 2 5.693 1.30 3 13.056 0.80 1.77250 49.6 4 4.734 2.13 5 7.040 2.00 1.80518 25.5 6 10.692 Variable 7 1.00 2 8 6.267 2.20 1.60311 60.7 9 -17.740 0.10 10 5.672 2.40 1.58913 61.2 11 -16.316 0.70 1.74000 28.2 12 3.249 0.43 13 7.879 1.40 1.60342 38.0 14 -33.197 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of fourth embodiment Surface 3 8 D 4.831E-4 -6.299E-4 E 1.833E-5 -1.691E-6 F -8.488E-7 -1.255E-6 G 3.646E-8 5.644E-8 Zoom interval of fourth embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.001 7.471 8.657 F/NO 2.091 3.019 3.270 d6 13.070 2.657 1.699 d14 1.000 5.166 6.276 Value of conditional expression of fourth embodiment fW/|f1| 0.40 (r2+r4)/2/|f1| 0.79 r5/|f1| 0.94 (νL1+νL2)/2-νL3 27.1 r10/f2 0.82 r12/f2 0.47 Fifth embodiment Group Surface r d n ν 1 1 12.636 1.00 1.67790 55.5 2 5.779 2.24 3 14.549 0.80 1.69680 55.6 4 4.557 1.98 5 5.791 2.00 1.75520 27.5 6 7.453 Variable 7 1.00 2 8 5.508 2.10 1.56883 56.0 9 -33.958 0.10 10 5.738 2.50 1.60311 60.7 11 -7.244 0.70 1.74000 28.2 12 3.581 0.38 13 8.806 1.40 1.68893 31.1 14 -24.167 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of fifth embodiment Surface 1 10 D 1.927E-4 -8.338E-4 E 3.203E-6 -4.188E-5 F -9.790E-8 -2.641E-6 G 2.362E-9 -1.390E-7 Zoom interval of fifth embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 7.528 8.672 F/NO 2.041 2.916 3.141 d6 13.070 2.607 1.694 d14 1.000 5.158 6.211 Value of conditional expression of fifth embodiment fW/|f1| 0.40 (r2+r4)/2/|f1| 0.68 r5/|f1| 0.77 (νL1+νL2)/2-νL3 28.1 r10/f2 0.83 r12/f2 0.52 Sixth embodiment Group Surface r d n ν 1 1 37.045 1.00 1.66547 55.2 2 5.700 1.42 3 15.012 0.80 1.77250 49.6 4 4.887 1.65 5 6.918 2.00 1.80518 25.5 6 12.616 Variable 7 1.00 2 8 6.330 2.50 1.60602 57.4 9 -14.092 0.10 10 12.616 2.20 1.58913 61.2 11 -12.616 0.60 1.75520 27.5 12 4.688 0.36 13 10.181 1.80 1.58144 40.8 14 -10.181 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of sixth embodiment Surface 1 8 9 D 3.895E-4 -8.516E-4 -3.907E-5 E 1.316E-6 -7.125E-7 -1.100E-6 F -5.517E-8 -6.206E-6 -6.200E-6 G 9.98E-10 1.937E-7 2.532E-7 Zoom interval of sixth embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 6.912 8.700 F/NO 2.067 2.789 3.170 d6 13.301 3.091 1.482 d14 1.000 5.031 7.056 Value of conditional expression of sixth embodiment fW/|f1| 0.43 (r2+r4)/2/|f1| 0.76 r5/|f1| 1.00 (νL1+νL2)/2-νL3 26.9 r10/f2 1.62 r12/f2 0.60 Seventh embodiment Group Surface r d n ν 1 1 40.183 1.00 1.66547 55.2 2 5.700 1.47 3 16.306 0.80 1.77250 49.6 4 4.887 1.33 5 6.574 2.00 1.80518 25.5 6 12.616 Variable 7 1.00 2 8 6.152 2.40 1.60602 57.4 9 -15.124 0.10 10 10.896 2.00 1.58913 61.2 11 -10.896 0.80 1.68893 31.1 12 4.326 0.44 13 11.234 1.60 1.51823 59.0 14 -11.234 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of seventh embodiment Surface 1 8 9 D 3.618E-4 -8.116E-4 4.008E-5 E 7.327E-7 6.994E-6 9.534E-6 F -5.614E-8 -4.319E-6 -4.695E-6 G 1.2394-9 7-020E-8 1.264E-7 Zoom interval of seventh embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 6.855 8.559 F/NO 2.079 2.836 3.178 d6 14.195 4.104 2.540 d14 1.000 5.009 6.962 Value of conditional expression of seventh embodiment fW/|f1| 0.44 (r2+r4)/2/|f1| 0.77 r5/|f1| 0.96 (νL1+νL2)/2-νL3 26.9 r10/f2 1.39 r12/f2 0.55 Eighth embodiment Group Surface r d n ν 1 1 43.546 1.50 1.66793 55.3 2 5.559 1.51 3 15.138 0.80 1.77250 49.6 4 4.861 1.33 5 6.467 1.70 1.80518 25.5 6 12.339 Variable 7 1.00 2 8 6.337 2.40 1.60602 57.4 9 -14.789 0.10 10 10.162 2.00 1.58913 61.2 11 -10.162 0.82 1.68649 30.9 12 4.271 0.46 13 11.401 1.60 1.51823 59.0 14 -11.401 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of eighth embodiment Surface 1 8 9 D 3.633E-4 -8.826E-4 -1.189E-4 E -2.708E-6 2.301E-5 3.012E-5 F 1-001E-7 -8.040E-6 -9.532E-6 G -1.263E-9 2.076E-7 3.420E-7 Zoom interval of eighth embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 6.855 8.559 F/NO 2.083 2.844 3.190 d6 14.195 4.104 2.540 d14 1.600 6.009 7.962 Value of conditional expression of eighth embodiment d1/fW 0.50 fW/|f1| 0.44 (r2+r4)/2/|f1| 0.76 r5/|f1| 0.94 (νL1+νL2)/2-νL3 26.9 r10/f2 1.30 r12/f2 0.55 Ninth embodiment Group Surface r d n ν 1 1 39.250 1.20 1.66793 55.3 2 5.700 1.47 3 16.306 0.80 1.77250 49.6 4 4.887 1.33 5 6.574 1.70 1.80518 25.5 6 12.616 Variable 7 1.00 2 8 6.152 2.40 1.60602 57.4 9 -15.124 0.10 10 10.896 2.00 1.58913 61.2 11 -10.896 0.82 1.68649 30.9 12 4.300 0.45 13 11.234 1.60 1.51823 59.0 14 -11.234 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of ninth embodiment Surface 1 8 9 D 3.888E-4 -8.333E-4 8.804E-6 E -4.405E-6 3.249E-5 4.337E-5 F 1.680E-7 -8.470E-6 -1.022E-5 G -1.860E-9 2.786E-7 4.034E-7 Zoom interval of ninth embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.008 6.874 8.581 F/NO 2.079 2.834 3.176 d6 14.195 4.102 2.539 d14 1.600 6.028 8.016 Value of conditional expression of ninth embodiment d1/fW 0.40 fW/|f1| 0.44 (r2+r4)/2/|f1| 0.77 r5/|f1| 0.95 (νL1+νL2)/2-νL3 26.9 r10/f2 1.39 r12/f2 0.55 Tenth embodiment Group Surface r d n ν 1 1 73.839 2.00 1.66793 55.3 2 5.942 1.17 3 12.779 0.80 1.77250 49.6 4 4.737 1.64 5 6.594 1.70 1.80518 25.5 6 11.293 Variable 7 1.00 2 8 6.434 2.40 1.60602 57.4 9 -13.616 0.10 10 10.374 2.00 1.58913 61.2 11 -10.374 0.82 1.68649 30.9 12 4.294 0.46 13 11.783 1.60 1.51823 59.0 14 -11.783 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspheric surface factor of tenth embodiment Surface 1 8 9 D 3.587E-4 -9.560E-4 -1.744E-4 E -4.139E-6 1.731E-5 2.388E-5 F 1.630E-7 -7.426E-6 -8.925E-6 G -2.370E-9 1.227E-7 2.705E-7 Zoom interval of tenth embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 6.855 8.559 F/NO 2.088 2.854 3.203 d6 14.195 4.104 2.540 d14 1.600 6.009 7.962 Value of conditional expression of tenth embodiment d1/fW 0.67 fW/|f1| 0.44 (r2+r4)/2/|f1| 0.78 r5/|f1| 0.96 (νL1+νL2)/2-νL3 26.9 r10/f2 1.32 r12/f2 0.55 Eleventh embodiment Group Surface r d n ν 1 1 15.775 1.00 1.67790 55.5 2 5.377 1.68 3 13.621 1.00 1.77250 49.6 4 4.729 1.85 5 6.822 2.00 1.80518 25.5 6 11.155 Variable 7 1.00 2 8 6.335 2.20 1.60311 60.7 9 -16.317 0.10 10 5.791 2.40 1.58913 61.2 11 -13.253 0.70 1.74000 28.2 12 3.308 0.41 13 7.774 1.40 1.60342 38.0 14 -40.735 Variable 3 15 ∞ 4.50 1.51633 64.1 16 ∞ - Aspherlc surface factor of eleventh embodiment Surface 3 8 D 4.148E-4 -6.404E-4 E 3.267E-5 4.942E-6 F -1.663E-6 -2.560E-6 G 5.433E-8 1.326E-7 Zoom interval of eleventh embodiment for 2-m object point Wide-angle end Standard position Telephoto end f 3.000 7.471 8.658 F/NO 2.098 3.039 3.294 d6 13.070 2.657 1.699 d14 1.000 5.166 6.276 Value of conditional expression of eleventh embodiment d3/fW 0.33 |f1|/fW 0.40 (r2+r4)/2/|f1| 0.67 r5/|f1| 0.91 (νL1+νL2)/2-νL3 27.1 r10/f2 0.83 r12/f2 0.48

Claims: A wide-angle aspheric zoom lens comprising a first lens group (1) having a negative refracting power and a second lens group (2) having a positive refracting power which are arranged in this order from a photographing object side to perform zooming by changing an aerial interval between the first and second lens groups, wherein both the first and the second lens groups have one or more aspheric surfaces; the first lens group comprises two meniscus negative lenses (L1) and (L2) each of which image side is concave and a positive lens (L3) whose object side is convex which are arranged in this order from the photographing object side; the first lens group meets the condition (1) 0.3 < fW/ f1 < 0.5; the second lens group comprises a positive lens (L4) whose object and image sides are convex, a combined lens (L5, L6) comprising a positive lens (L5) whose object side is convex, and a negative lens (L6) whose image side is concave, and a positive lens (L7) whose object side is convex which are arranged in this order from the photographing object side, characterized in that the combined lens in the second lens group (2) is a cemented lens (L5,L6); the first lens group (1) further meets the following conditions, (2) 0.6 < (r2 + r4)/(2 f1 ) < 1.0 (3) 0.7 < r5/ f1 < 1.5 (4) 20 < (νL1 + νL2)/2 - νL3 where, in the above expressions, fW represents a focal length at a wide angle end; fl represents a focal length of the first lens group (1); r2, r4, and r5 represent the radiuses of curvature of an image-side surface of the first lens (L1) of the first lens group, an image-side surface of the second lens (L2) of the first lens group, and an object-side surface of the third lens (L3) of the first lens group. respectively; and νL1, νL2, and νL3 represent the respective Abbe numbers; and the second lens group (2) meets the following conditions, (5) 0.6 < r10/f2 < 3.0 (6) 0.4 < r12/f2 < 0.8 where, in the above expressions, f2 represents a focal length of the second lens group (2) and r10 and r12 represent the radiuses of curvature of the object side of the positive lens (L5) comprised in the combined lens in the second lens group (2) and the image side of the negative lens (L6) comprised in the combined lens in the second lens group (2), respectively. A video camera using the wide-angle aspheric zoom lens according to claim 1. The wide-angle aspheric zoom lens according to claim 1, wherein the second lens (L5) from the photographing object side of the second lens group (2) is a positive lens whose object and image sides have the same radius of curvature. The wide-angle aspheric zoom lens according to claim 1, wherein the fourth lens (L7) form the photographing object side of the second lens group (2) is a positive lens whose object and image sides have the same radius of curvature. The wide-angle aspheric zoom lens according to claim 1, wherein the first lens (L1) from the photographing object side of the first lens group (1) has one or more aspheric surfaces and meets the following condition, (7) d1 / fW > 0.35 where in the above expression, d1 represents a center thickness of the first negative lens (L1) of the first lens group (1) and fW represents a focal length at the wide-angle end. The wide-angle aspheric zoom lens according to claim 1, wherein the second lens (L2) from the photographing object of the first lens group (1) has one or more aspheric surfaces and meets the following condition, (8) d3 / fW > 0.3 where, in the above expression, d3 represent a center thickness of the second negative lens (L2) of the first lens group (1) and fW represents a focal length at the wide-angle end.

Inventors: NAKAJIMA YASUO, OKAYAMA HIROAKI, ONO SHUSUKE, NAKAJIMA, YASUO, OKAYAMA, HIROAKI, ONO, SHUSUKE
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: G02B13
IPC codes: G02B15, G02B13